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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

152

HYDRAULIC LIMES AND CEMENTS

HYDRAULIC  LIMES   AND   CEMENTS

The chief of these products are furnished by the kilning of argillaceous
limestone or marl or mixtures of these with each other or with clay. Among
them arc : Hydraulic lima, which is whitish or yellowish and causes sneezing
when its powder is diffused sparsely in the air ; natural rapid-setting cement
or Roman cement, dark yellow or greyish yellow ; natural slow-setting cement
or natural Portland cement, and artificial (or true] Portland, cement, dark
grey, often inclining to greenish. Other forms of cement are (trap-pier's
cement, made from the argillaceous residues from the slaking of hydraulic
lime, and of whitish colour ; slag cements, intimate mixtures of blast-furnace
slag with lime, grey in colour, and mixed cements.

The testing of these products includes chemical analysis and, what is
of greater practical importance, certain technical tests described later.

1.   Chemical Analysis

The more; important determinations to be made with hydraulic limes
and with cements are : loss on ignition (water plus carbon dioxide), total
silica, alumina plus ferric oxide, lime and magnesia, In some; cases esti-
mations are required of the carbon dioxide, the sand separately from the
combined silica, ferric oxide separately from alumina, sulphates (gypsum)
and, in slag cements, sulphides (calcium sulphide), All these deti-nninatlons
arc made by the methods already described in considering limestones and
marls.

Sometimes, in order to detect the presence of lie/ei'ogciieons materials
(e.g., of slag in a Portland cement), it is convenient, to analyse separately
the finer parts (passing through a sieve with .|,(joo meshes per sq. cm.) and
the coarser ones : any appreciable diflVivnce indicates addition of extraneous
material.

To the determinations mentioned above, that of the alkalinity (free
lime), carried out as follows, is sonu'fhm-s added : i gram of the finely
powdered material is shaken for 10 minutes with 100 c.r. of distilled water
and filtered, 50 c.c, of the lilt rate being titrated with N/io hydrochloric
acid.

From the results of the elu-niieal analysis it is usual to calculate the
relations between tin- principal components. The hydraulic index is the
ratio, (silica 4- alumina,) : lime ; according to some, the ferric oxide also
is added to the alumina,, while, according to others, the magnesia should
be addc'd to the lime, owing to ana logo us functions in the se-tting. The
hydraulic modulus of Miehaelis is the inverse ratio, namely, lime : (silica, +
alumina 4- ferric; oxide).

2.  Technical Tests

The chief of these are as follows :

1. Ocular Examination. -This is math- with a lens and may detect
the presence of extraneous matter, such as particles of coal, sand, slag,
gypsum, i-tc,ally not less